Minimally invasive sensing systems are routinely utilized by medical professionals to evaluate, measure, and diagnose conditions within the human body. As one example, intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing a diseased vessel, such as an artery, within the human body to determine the need for treatment, to guide the intervention, and/or to assess its effectiveness. An IVUS device includes one or more ultrasound transducers arranged at a distal end of an elongate member. The elongate member is passed into the vessel thereby guiding the transducers to the area to be imaged. The transducers emit ultrasonic energy in order to create an image of the vessel of interest. Ultrasonic waves are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. Echoes from the reflected waves are received by the transducer and passed along to an IVUS imaging system. The imaging system processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the device is placed.
There are two general types of IVUS devices in use today: rotational and solid-state (also known as synthetic aperture phased array). For a typical rotational IVUS device, a single ultrasound transducer element is located at the tip of a flexible driveshaft that spins inside a plastic sheath inserted into the vessel of interest. The transducer element is oriented such that the ultrasound beam propagates generally perpendicular to the axis of the device. The fluid-filled sheath protects the vessel tissue from the spinning transducer and driveshaft while permitting ultrasound signals to propagate from the transducer into the tissue and back. As the driveshaft rotates, the transducer is periodically excited with a high voltage pulse to emit a short burst of ultrasound. The same transducer then listens for the returning echoes reflected from various tissue structures. The IVUS imaging system assembles a two dimensional display of the vessel cross-section from a sequence of pulse/acquisition cycles occurring during a single revolution of the transducer.
In contrast, solid-state IVUS devices utilize a scanner assembly that includes an array of ultrasound transducers distributed around the circumference of the device connected to a set of transducer controllers. The transducer controllers select transducer sets for transmitting an ultrasound pulse and for receiving the echo signal. By stepping through a sequence of transmit-receive sets, the solid-state IVUS system can synthesize the effect of a mechanically scanned transducer element but without moving parts. Since there is no rotating mechanical element, the transducer array can be placed in direct contact with the blood and vessel tissue with minimal risk of vessel trauma. Furthermore, because there is no rotating element, the interface is simplified. The solid-state scanner can be wired directly to the imaging system with a simple electrical cable.
Conventional rotational IVUS catheters are interfaced to the non-rotating or stationary part of the IVUS imaging system by means of a rotary transformer. The rotary transformer is comprised of two sections: a rotating section that is mounted on the shaft of a motor that rotates the catheter driveshaft and a non-rotating section that is mounted in close proximity to the rotating section. The two sections are separated by an air gap. AC signals are transmitted across this rotating interface by means of transformer action. Rotational IVUS catheters that have a piezoelectric zirconate transducer (PZT) can be implemented with transmission of only AC signals (e.g., excitation signals to the PZT element and/or return signals from the PZT element to the IVUS console). However, catheters with advanced transducer technologies, such as piezoelectric micromachined ultrasonic transducers (PMUT), include electronic components that require DC power. Since a rotary transformer couples only time varying signals, it cannot be used to transmit a DC signal or voltage to the rotating side of the imaging system.
Thus, while existing rotary interfaces have proved useful, there remains a need for improvements in the design to allow advanced transducer technologies to be implemented. Accordingly, the need exists for improvements to the interface module of the rotational IVUS imaging system.